Dăm ba mấy dạng kiểu này
Cô si vài cái có gì khó khăn !
\(P=\frac{3yz}{x}+\frac{4xz}{y}+\frac{5xy}{z}\)
\(=\left(\frac{yz}{x}+\frac{zx}{y}\right)+2\left(\frac{yz}{x}+\frac{xy}{z}\right)+3\left(\frac{zx}{y}+\frac{xy}{z}\right)\)
\(\ge2z+3y+6x\)
\(=2\left(x+z\right)+4\left(x+y\right)\)
\(\ge4\sqrt{xz}+8\sqrt{xy}\)
\(=4\left(\sqrt{xz}+2\sqrt{xy}\right)\)
\(=4\)
Dấu "=" xảy ra tại \(x=y=z=\frac{1}{3}\)
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